I mostly use Google because I've been using it for so long that it's almost integrated into my browser (Firefox). I have so many quick searches tools and shortcuts that point to Google that it would be more trouble than it's worth to change them.
I give Google as little information as I can and I have turned off my search history. I don't trust it.
I use Google calendar. It doesn't have much personal information. And I have a Gmail account that I use mainly for storing files. If I want to permanently store a big file I compress and encrypt it and sent it to my Gmail address.
I use Bing and Yahoo every now and then because I don't allow then to store cookies. I like duck duck go because it uses Google's search engine but it also doesn't know who I am.